"The sun is out, and so are the Tories," declared an apparently jubilant Neil Kinnock on the morning of polling day 1992; but in fact the Tories hung on. Psephologists might easily pore for most of the next decade over the link between good or bad weather and electoral outcomes without reaching any settled conclusion. It is often assumed that turnout goes up in fine weather, but that isn't necessarily so. It fell to its lowest level since 1935 on a day when the sun was out and Labour were in – 1 May 1997.

If, using British Electoral Facts, by Colin Rallings and Michael Thrasher, you check the pattern of election day weather since 1918, a tentative conclusion could be that good weather today might benefit David Cameron. On the seven election days since 1945 where the people threw the government out, five took place in fair or good weather. To put it another way, of nine elections in the same period where the weather was fair or good across most of the country, six saw the incumbents ousted. The Conservatives won on good weather days in 1951 (light fog and frost first thing, but generally fair), 1955, 1959 ("a dry autumn day"), 1970 ("fine everywhere"), 1979 ("fair") and 1992. Labour came home in sunshine in 1945 (though many votes were cast then by servicemen in uncharted weather abroad), 1966 ("a mild day") and 1997 ("sunny and dry"). Some may deduce that this has something to do with the laws of meteorology; others, that it rather reflects the laws of coincidence.

It seems on the whole surprising, given the reputation of Britain's weather, that few elections since 1918 have taken place in foul weather. The worst on this list would appear to be 1918, 1924, 1964 (rain over much of the country) and 1987 (dry and sunny in western districts, but elsewhere, rain, sometimes with thunderstorms). Today's forecast – rain in Wales spreading to most of England, drier and brighter elsewhere – is as intriguingly poised as the contest itself appears to be.

If polling days have come to seem more clement occasions, that is because they are usually nowadays staged in the spring or summer. Between 1918 and the end of 1974, 12 elections out of a total of 17 took place between early October and the end of February. All eight since then have been timed for April, May, June or July. And always on Thursday – a practice governed by no hard and fast rule but the steady preference for 75 years. Before that, Tuesday was chosen in 1931, Wednesday in 1922 and 1924, while 1918 saw a contest on a Saturday. Maybe now that the people of Britain are thought to be thirsty for change, the time may shortly arrive when, as with the Epsom Derby, midweek dates are abandoned in favour of the weekend.